Here’s yet another reason to consider dogs man’s — and woman’s — best friend. University of Illinois researchers are studying genetic similarities between some dog and human cancers — work they say may allow pet dogs to serve as useful models for studying new chemotherapies.

University of Illinois veterinary clinical medicine professor Timothy Fan said pet dogs with naturally occurring cancers — rather than laboratory-induced tumors — are better subjects for early cancer drug trials.

In a meeting of the National Cancer Policy Forum of the National Academies' Institute of Medicine in Washington, D.C., Fan and 15 other experts in the field suggested canine cancers develop in ways that are markedly similar to human forms of the disease.

"We have a lot of dogs in the United States, approximately 70 million of them, and it's believed that about 25 percent of pet dogs will develop some form of cancer in their lifetime," Fan said. "We're using dogs to help guide drug development for people, but at the same time we're offering new, innovative therapies that would otherwise never be available to dogs, to help them as well."

Several attributes make pet dogs perfect subjects such studies, Fan said.

"Dogs tend to develop cancer as a geriatric population, just like people," he said. "Because the tumors develop spontaneously, there is heterogeneity in that tumor population, as a human being would have. The size of the tumors and the speed of growth of those tumors are comparable in dogs and human beings. So there are many attributes of a dog that develops cancer spontaneously that recapitulate the biology that we see in people."

Some studies have already begun using dogs to test new cancer therapies. Eight years ago, Fan demonstrated the effectiveness of an anti-cancer drug called PAC-1 (developed by UI chemistry professor Paul Hergenrother) in pet dogs with naturally occurring lymphomas and osteosarcomas. The results in dogs allowed the scientists to begin studying the drug as a potential therapy against human cancers in new clinical trials.

Other experimental cancer drugs first tested in pet dogs include muramyl tripeptide, an immune-stimulating agent that could not be tested in immune-deficient mice or rats with induced cancers, Fan said.

"Because you're taking a human cancer tissue and implanting it in a mouse, that's a foreign tissue, and the mouse's immune system will reject it," he said. "So you have to transplant those tissues into an immunocompromised mouse. Dogs are immunocompetent, and so were an ideal study subject for testing immunomodulatory cancer therapies.”